The Fourth Amendment protects you and your property from unreasonable search and seizure by the government and its agents -- not private third parties. Although the "Fed" in FedEx may confuse you, this package carrier is a private entity. FedEx doesn't need a warrant to rifle through your packages, so don't try FedExing weed.
Explanation
The Sixth Amendment right to a jury of your peers doesn't specifically guarantee any number of jurors on a criminal jury, but the Supreme Court has determined that criminal juries of less than six violate this protection.
It may sound strange, but a federal court actually found that California's Death Row system was so backlogged that it violated the Eighth Amendment prohibition against cruel and unusual punishment.
The First Amendment protects individuals from government intervention on their speech or expression. Private companies like Facebook can remove posts as they see fit, and you can be fired from a private company for tweeting without implicating your First Amendment rights.